The present invention relates to a process for producing a modified polymer rubber, which comprises simple steps. Since said modified polymer rubber has superior impact resilience, it is capable of producing motorcar tires having superior fuel cost saving.
A styrene-butadiene copolymer obtained by emulsion polymerization is known as rubber used for motorcar tires. However, said copolymer has a problem that motorcar tires comprising said copolymer are unsatisfactory from a viewpoint of fuel cost saving, because the copolymer has insufficient impact resilience.
In order to obtain rubber having superior impact resilience, (1) JP-B 5-46365 discloses a process, which comprises copolymerizing butadiene and styrene in a hydrocarbon solvent using an organolithium compound as an initiator, and a Lewis base such as ether as a microstructure controlling agent, and (2) Japanese Patent No. 2540901 proposes a process, which comprises reacting an alkali metal bound at the end of a diene polymer rubber with a specific acrylamide, thereby obtaining a modified diene polymer rubber having improved impact resilience.
However, the above-mentioned processes have a problem that it is difficult to (1) introduce satisfactory number of polar groups, and (2) control strictly positions at which the polar groups are introduced.
Further, while a level of a demand for fuel cost saving of motorcar tires is recently higher from an environmental view, any of the above-mentioned copolymer rubbers can hardly meet such a demand.
An object of the present invention is to provide a process comprising simple steps for producing a modified polymer rubber having superior impact resilience, which modified polymer rubber is accordingly capable of producing motorcar tires having superior fuel cost saving.
The present invention provides a process for producing a modified polymer rubber, which comprises the steps of:
(1) reacting one part by mol of an organoalkali metal compound with nxc2x10.7 (n is an integer of 3 or more) parts by mol of a compound represented by the following formula (1) to produce a reaction mixture, 
wherein R1 is an amino group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group, a mercapto group or a derivative thereof (hereinafter referred to as xe2x80x9cstep (1)xe2x80x9d),
(2) polymerizing in the presence of the produced reaction mixture an aromatic vinyl monomer and a conjugated diene monomer in a hydrocarbon solvent, and after completion of the polymerizing, stirring for at least 30 minutes, to produce a polymerization reaction mixture (hereinafter referred to as xe2x80x9cstep (2)xe2x80x9d), and
(3) repeating such an operation nxe2x88x922 times that (i) an aromatic vinyl monomer and a conjugated diene monomer are added to the produced polymerization reaction mixture, and polymerized, and (ii) after completion of the polymerizing, stirring is carried out for at least 30 minutes, and thereby producing a modified polymer rubber, whose both ends and nxe2x88x922 positions in its chain are modified by the compound represented by the formula (1) (hereinafter referred to as xe2x80x9cstep (3)xe2x80x9d).
The present invention also provides a process for producing a modified polymer rubber, which comprises the steps of:
(1) reacting one part by mol of an organoalkali metal compound with nxc2x10.7 (n is an integer of 3 or more) parts by mol of a compound represented by the above-mentioned formula (1) to produce a reaction mixture (hereinafter referred to as xe2x80x9cstep (1)xe2x80x9d).
(2) polymerizing in the presence of the produced reaction mixture an aromatic vinyl monomer and a conjugated diene monomer in a hydrocarbon solvent, and after completion of the polymerizing, stirring for at least 30 minutes, to produce a polymerization reaction mixture (hereinafter referred to as xe2x80x9cstep (2)xe2x80x9d),
(3) repeating such an operation nxe2x88x922 times that (i) an aromatic vinyl monomer and a conjugated diene monomer are added to the produced polymerization reaction mixture, and polymerized, and (ii) after completion of the polymerizing, stirring is carried out for at least 30 minutes, and thereby producing a modified polymer rubber, whose both ends and nxe2x88x922 positions in its chain are modified by the compound represented by the formula (1) (hereinafter referred to as xe2x80x9cstep (3)xe2x80x9d), and
(4) modifying further the produced modified polymer rubber with a modifier having a functional group, and thereby producing a modified polymer rubber, whose initial end is modified by the compound represented by the formula (1), whose terminal end is modified by two functional groups, wherein one of said two functional groups is derived from the compound represented by the formula (1), and another thereof is derived from the modifier, and each of nxe2x88x922 positions in whose chain is modified by one functional group of the compound represented by the formula (1) (hereinafter referred to as xe2x80x9cstep (4)xe2x80x9d).